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Wednesday, 7 November 2012

Talk : Carbon Capture Technology

A recent talk in this seasons series of Café Scientifique talks was entitled “Carbon Capture and Storage and Decarbonising Electricity” and presented by Prof. Trevor Drage from the Faculty of Engineering at the University of Nottingham. (you can see his research page here)

The talk discussed Carbon Capture and Storage (CCS) technology, which is potentially a key plank in enabling the UK government to achieve their aim of achieving a 80% reduction in CO2 emissions (compared to 1990 levels) by 2050 and the de-carbonisation of electricity generation by 2030 (see here Notts based research in this area).

The scale of the task that the UK has committed to can be gauged from the three charts below (taken from the Fourth carbon budget report) which show the reduction of “carbon intensity” that will be required, and also the amount of existing capacity that will need to be replaced, due to the age of the power stations, in the same timeframe (both taken from the Fourth Carbon Budget report, which is a genuinely fascinating
read.

The Targets committed to are ambitious

...and need to be achieved with much of the UK's generating capacity retireing over the coming decades

Off-Shore Wind is perhaps the biggest potential growth area

CCS aims to remove the carbon dioxide produced from fossil fuel burning and store it deep underground so that it does not contribute to increasing atmospheric CO2 levels and climate change.

A less mature technology than technologies such as wind or nuclear, CCS may allow the UK to continue using fossil fuels whilst simultaneously reducing CO2 emissions.

The diagram below outlines the main parts of a typical CCS installation, as it might be implemented in the UK. Fossil fuel is mined and burnt in a power station as usual, but the CO2 is extracted from the process and transported to a location where it can be buried 1-2km below the earth’s surface in rock formations that are able to hold the CO2 for, at least, hundreds of years. The geological structures under the North Sea, which formerly held stocks of crude oil, are ideal for this application.

Incidentally, the CO2 does not sit in the rocks as a big bubble, but rather is partly dissolved in the water that is in the rocks and also partly forms tiny capillary bubbles in the pores of the rocks. There is some possibility that, over long periods of time, the CO2 may mineralise - which would certainly ensure that it stayed where it was put!

Post-combustion capture : This is the method that would be applied to most conventional power plants. Here, carbon dioxide is captured, or “scrubbed”(‘scrubbed') from the combustion exhaust, leaving just water and Nitrogen to be emitted back to the atmosphere. It is worth noting that this technology is already in use (albeit on a much smaller scale) in many other industrial applications.

Oxy-fuel process : In this approach, the Nitrogen is first removed from the air, leaving almost pure Oxygen, and it is this oxygen that is used to burn the fuel. The use of pur oxygen results in only two reaction products - CO2 and water - which are easily separated.

Pre-Combustion Process : This is a bit trickier to understand (not least for NSB). Like the Oxy-fuel process, the incoming air is processed to remove the Nitrogen, leaving almost pure oxygen. But then the oxygen is used to “gasify” the fuel, producing Hydrogen and CO2. The CO2 can be relatively easily separated out, leaving the Hydrogen to be used as a fuel that reacts with Air to produce only water as a reaction product.

It is worth mentioning that there are a number of different methods of separating the CO2 from a gas mixture, ranging from absorption by another material to membrane separation to Bio-reactors that use the CO2 as food.

One question that many people, quite reasonably, have regarding this technology is its cost and also the impact that is has on the overall efficiency of the power station (as energy is required to power all the CO2 separation, compression and transport parts of the process. Prof Drage explained that CCS technology was currently more expensive than nuclear or on-shore wind, but cheaper than off-shore wind power, adding that the CO2 carbon trading market, which values CO2 at 30 Euros per tonne, was a big factor in making CCS technology economically viable.

He also pointed out the CCS was not really appropriate as a retro-fit for older power stations, such as Radcliffe-on-soar, which only operate at perhaps 35% efficiency. Instead, it made more sense to add it to the latest generation of new build power stations, which operate at around 48% - a figure that reduced to around 40% once CCS equipment has been installed.

Of the many technical terms in this unusually acronym rich document, the following are perhaps worth noting:

Levelised : the price at which electricity must be generated from a specific source to break even over the lifetime of the project. It is an economic assessment of the cost of the energy-generating system including all the costs over its lifetime: initial investment, operations and maintenance, cost of fuel, cost of capital, and is very useful in calculating the costs of generation from different sources

FOAK : “First of a Kind” - acknowledgement that costs are higher for the first examples of a particular technology.

NOAK : “Nth of a Kind” (!!) - costs once a technology has become mature.

The document, quite sensibly, includes a number of caveats to its conclusions, some of which are shown below, in addition to these it is worth mentioning that future fuel prices (which are far from clear) can have a big influence on the relative costs of different generating technologies.

“The cost estimates are generally for base-load energy on common assumptions of load factor (though wind is constrained by energy availability), and as such we are ignoring the issue of despatch risk which depends on the plant’s expected merit position over its life. No consideration is provided here for differences between technologies for the requirements for reserve and balancing services, or in terms of transmission network reinforcement impacts.

We have not commented on (or quantified) the vulnerability of particular technologies to fuel supply and other interruptions, which varies considerably between technologies.

Embedded benefits for smaller scale generators connected to the distribution networks are not considered.

Externalities relating to environmental and social impacts of construction, operation and fuel supply chains are excluded, except to the extent that they are internalised through the carbon price.

Costs and relative ranking is heavily influenced by assumptions on fuel and carbon

…[In the real world] developers factor in risk premiums, the appetite of lenders and the broader impacts on their own corporate financial positions. Once these factors are considered [Gas] and onshore wind projects are often easier to finance than most other technologies.”

In terms of actual working plants, Dr Drage mentioned a plant in Ferrybridge that is capturing a small percentage of its carbon emissions as a technology demonstrator, a similar plant that has been running in China for some 8 years and an operational plant in Canada.

Some countries, India for example, are not keen on CCS because their overwhelming priority is to introduce new capacity and they do not want to be burdened with losing some of this new capacity to power CCS.

Lastly, Prof Drage mentioned that the Department of Energy and Climate Change have an on-line interactive model where you can adjust the UK’s energy mix and how energy is consumed with the aim of meeting climate change act carbon target. NSB has had a go and recommends it unreservedly.

Rating on the NSB Science Accessability Criteria.
Where NSB has actually attended the talk (as opposed to getting a set of slides afterwards), NSB is able to rate the talk according to the "NSB Science Accessability Criteria" questions, and has done so on this occasion, with results shown below:

1) Does the organisation have a central list of all events? Yes
2) It is clear, before the talk starts , whether the slides will be available on the Internet or by email? No
3) Are links provided for people to find out more information? No
4) Are papers that are referred easily accessible, in full, to the public? N/A not many papers referred to in talk (which is fine, btw)

Image SourceEnergy Report ChartsCCS Schematic
NB: All the images on this post should be expandable by clicking on them. If this doesn't work for you, please let me know. Ta

1 comment:

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